<!DOCTYPE html>
<html lang="en" >
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<div id="app">
  <h2>当前计数:{{counter}}</h2>
  <button @click="add">+</button>
  <button @click="sub">-</button>
</div>

<script src="../js/vue.js"></script>
<script>
  const app = new Vue({
    el: '#app',
    data: {
      counter: 0
    },
    methods: {
      add() {
        this.counter++;
      },
      sub() {
        this.counter--;
      }
    }
  })
  app.counter++;
</script>
</body>
</html>
